This invention relates to fire doors which utilize spring tension to effect their automatic closure in the event of a fire and, more particularly, to a hold and release mechanism for the spring tension adjusting wheel for such a door.
Modern building codes for certain types of buildings require the presence of fire doors. The fire doors are arranged to automatically close upon the sensing of a fire condition in the vicinity of the door, so as to prevent the fire from spreading. Conventionally, such doors are associated with stored mechanical energy, such as, for example, a pretensioned spring or a raised weight, which is releasable to effect closure of the door. A typical release mechanism includes a fusible link which melts in the presence of fire to allow portions of a holding chain, or cable, to separate in order to release the stored energy.
With such an arrangement, it is necessary to be able to adjust the spring tension when the door is installed. Accordingly, an operator accessible adjusting wheel is generally provided. This adjusting wheel is normally prevented from rotating by a locking mechanism coupled to the holding chain so that when tension is applied by the holding chain, the adjusting wheel is locked. However, when the fusible link melts and separates the holding chain, the mechanism frees the adjusting wheel for rotation to allow the stored spring tension to move the fire door. In the past, to adjust the spring tension, the operator would relieve the tension applied by the holding chain to the locking mechanism, turn the adjusting wheel in the direction opposite to that in which the adjusting wheel turns during closure of the fire door a sufficient number of turns to provide the appropriate spring tension, and then restore the tension applied by the holding chain to the locking mechanism. Typically, turning of the adjusting wheel was effected by means of a wrench gripping the hub of the adjusting wheel. Since it is common to utilize a large wrench to gain maximum mechanical advantage, such a wrench could typically not make a full rotation and would therefore have to be removed from the adjusting wheel hub, the adjusting wheel would have to be held from turning, and the wrench would have to be reoriented and replaced on the adjusting hub. Such operation is very difficult and often requires that two operators be involved.
It is therefore a primary object of the present invention to provide a hold and release mechanism for a fire door spring tension adjusting wheel which overcomes the disadvantages of the conventional prior art locking mechanisms.
It is another object of the present invention to provide such a mechanism wherein the spring tension may be adjusted via the adjusting wheel without requiring that the holding chain tension be released.
It is a further object of this invention to provide such a mechanism which is designed so that a single operator can easily adjust the spring tension.